docs: def distance(lons1, lats1, depths1, lons2, lats2, depths2):
      """
      Calculate a distance between two points (or collections of points)
      considering points' depth.
  
      Calls :func:`geodetic_distance`, finds the "vertical" distance between
      points by subtracting one depth from another and combine both using
      Pythagoras theorem.
  
      :returns:
          Distance in km, a square root of sum of squares of :func:`geodetic
          <geodetic_distance>` distance and vertical distance, which is just
          a difference between depths.
      """
      hdist = geodetic_distance(lons1, lats1, lons2, lats2)
      vdist = depths1 - depths2
      return numpy.sqrt(hdist ** 2 + vdist ** 2)